Question

SQL gurus

I have a table structure as follows

Id        Name        IdPartner
Id1       name1           
Id2       Name2       Id1
Id3       name3       Id1
Id4       name4       Id2
Id5       name5       Id3

I need to write a query that would recursively loop through the table to find the partners.

I.e Given an Id say Id1 here, I need to pull out all the Names where Id1 is listed as a partner, So my query need to pull up Name3 and Name2. Subsequently in the same query I also need to pull the names where Name3 and Name2 are also listed as partners. So in this case if I give the input to the SP as Id1 I should effectively get a list that read as below

   Id          Name
  Id2         name2
  Id3         name3
  Id4         name4
  Id5         name5

I havent worked with recursively getting the data in SQL. Someone told me I could use a common table expression, but I fail to see how that would help me. I have been breaking my head over this for over a day and all I can come up with is the idea of using a cursor.

Any help in this regard helps

Answer 1

The following returns the related, but not requested, rows:

declare @Gurus as Table ( Id VarChar(4), Name VarChar(16), IdPartner VarChar(4) )
insert into @Gurus ( Id, Name, IdPartner ) values
  ( 'Id1', 'name1', NULL ),
  ( 'Id2', 'Name2', 'Id1' ),
  ( 'Id3', 'Name3', 'Id1' ),
  ( 'Id4', 'Name4', 'Id2' ),
  ( 'Id5', 'Name5', 'Id3' )

declare @TargetId as VarChar(4) = 'Id1'

; with RelatedGurus as (
  -- Anchor: Get the rows that are partners of the target row.
  select Id, Name, IdPartner
    from @Gurus
    where IdPartner = @TargetId
  union all
  -- Recursion: Add any rows that are partners to the rows just added.
  select G.Id, G.Name, G.IdPartner
    from @Gurus as G inner join
      RelatedGurus as RG on RG.Id = G.IdPartner )
  -- Display the result.
  select Id, Name
    from RelatedGurus
    order by Name